Remote imaging is a broad-based technology having a number of diverse and extremely important practical applications—such as geological mapping and analysis, military surveillance and planning, and meteorological forecasting. Aerial and satellite-based photography and imaging are especially useful remote imaging techniques that have, over recent years, become heavily reliant on the collection and processing of digital image data. Spatial data—characterizing real estate improvements and locations, roads and highways, environmental hazards and conditions, utilities infrastructures (e.g., phone lines, pipelines), and geophysical features—can now be collected, processed, and communicated in a digital format to conveniently provide highly accurate mapping and surveillance data for various civilian and military applications (e.g., dynamic GPS mapping).
A major challenge facing some such remote imaging applications is one of image resolution. Certain applications require very high image resolution—often with tolerances of inches. Depending upon the particular system used (e.g., aircraft, satellite, or space vehicle), an actual digital imaging device may be located anywhere from several hundred feet to several miles above its target, resulting in a very large scale factor. Providing images with very large scale factors, that also have resolution tolerances of inches, poses a challenge to even the most robust imaging system.
Orthophotography is one approach that has been used in an attempt to address this problem. In general, orthophotography renders an image of a target by compiling varying images of the target. Typically, in aerial imaging applications, a digital imaging device that has a finite range and resolution records images of fixed subsections of a target area sequentially. Those images are then aligned according to sequence to render a composite of a target area. Usually, conventional systems must make some trade-off between resolution quality and the size of area that can be imaged. If the system is designed to provide high-resolution digital images, then the field of view (FOV) of the imaging device is typically small. Numerous imaging iterations must be performed in order to orthographically render an image of a large area. If the system provides a larger FOV, then usually the resolution of the digital image is decreased and the distortion is increased.
Some conventional digital imaging systems have attempted to address these issues with large-scale single lens cameras. These cameras typically comprise a very large primary optical lens, behind which a number of optical sensors are embedded. The characteristics of these configurations, especially the optical properties of the primary lens, tend to render images of very small cross sectional area. Generally, sensors in these systems have either identical or coinciding lines of sight. Such systems are generally inefficient when images with wide FOV are desired. Furthermore, such systems are usually very costly. Rapid development of new sensor technologies renders these systems obsolete or requires that the systems have cumbersome and costly upgrades or modifications.
Other conventional systems have attempted to address the shortcomings of such primary lens configurations through the use of divergent sensor arrays. Usually, optical sensors are outwardly mounted along a convex brace or housing such that their focal axes diverge outwardly from the imaging device. Based on the intended scale factor for the images, the individual sensors in the array can be disposed such that their focal planes adjoin or slightly overlap at a desired distance from the target area. Although such a configuration can provide a wider FOV for imaging, it is still limited in application. The sensor arrays must be mounted within a host aircraft or spacecraft, and thus require a portal in the craft through which to obtain image data. Large sensor arrays require large portals to provide proper optical access for all the diverging sensors in the array. In many cases, however, large portal spaces are impractical, if not impossible, to provide within the small confines of a host craft. Furthermore, larger portals allow a relatively high degree of light backscatter in the array, causing ghost images and degrading the overall quality and reliability of the images obtained.
There is, therefore, a need for an imaging system that provides efficient and versatile imaging for different FOVs, especially very large FOVs, while maintaining image quality and clarity.